Nanoparticle-Supported, Rapid, and Electronic Detection of SARS-CoV-2 Antibodies and Antigens at Sub-Femtomolar Level

Major challenges remain to precisely detect low-abundance proteins from diverse biofluids in a rapid and cost-effective manner. Here we present a gold nanoparticle (AuNP)-supported, rapid electronic detection (NasRED) platform with sub-femtomolar sensitivity and high specificity. Surface-functionalized AuNPs act as multivalent detectors to recognize target antigens and antibodies through high-affinity binding, subsequently forming aggregates precipitated in a microcentrifuge tube and producing a solution color change. The optical extinction of residual floating AuNPs is digitized using a customized circuitry incorporating inexpensive optoelectronic elements and feedback mechanisms for stabilized readout. Uniquely, NasRED introduces active fluidic forces through engineered centrifugation and vortex agitation, effectively promoting protein detection at low concentrations and accelerating signal generation. Using SARS-CoV-2 as a demonstration, NasRED enables detection of both antibodies and antigens from a small sample volume (6 µL), distinguishes the viral antigens from those of human coronaviruses, and delivers test results in a short time (as fast as <15 min). The limits of detection (LoDs) for antibody detection are approximately 49 aM (7 fg/mL) in phosphate-buffered saline, or >3,000 times more sensitive than Enzyme-Linked Immunosorbent Assay (ELISA), ∼76 aM (11 fg/mL) in human pooled serum and in the femtomolar range in diluted whole blood. For nucleocapsid protein detection, NasRED LoDs are ∼190 aM (10 fg/mL) in human saliva and ∼2 fM (100 fg/mL) in nasal fluid. Unlike laboratory-based ELISA platforms, NasRED is a one-pot, in-solution assay that eliminates the needs for washing, labeling, expensive instrumentation or highly trained operators. With low reagent costs and a compact system footprint, this modular digital platform is well-suited for accurate, near-patient diagnosis and screening of a wide range of infectious and chronic diseases.